Spectral Analysis of the Acoustic Near Field of a Solid-Propellant Rocket

Abstract

Recently, Horne et al. (“Measurements of Unsteady Pressure Fluctuations in the Near-Field of a Solid Rocket Motor Plume,” International Journal of Aeroacoustics,Vol. 15, Nos. 4–5, July 2016, pp. 554–569) presented extensive measurements of the acoustic near field of a solid-propellant rocket. The experiment consists of two phases: the high-burn phase and the low-burn phase. The main objective of this investigation is to use this set of data for the determination of the dominant noise components in the near field of a rocket. The data consist of spectral measurements of an array of 14 near-field microphones and a single far-field microphone. By itself, this set of data is insufficient to accomplish the stated objective. The data are supplemented with information provided by the two-noise source model (Tam, C. K. W., Viswanathen, K., Ahuja, K. K., and Panda, J., “The Sources of Jet Noise: Experimental Evidence,” Journal of Fluid Mechanics, Vol. 615, 2008, pp. 253–292) of hot supersonic laboratory jets. The two-noise source model is supported by the existence of two similarity spectra. By applying the similarity spectra to the data of Horne et al. at low burn, it is shown that the dominant noise components in the near field of a solid-propellant rocket are the same as those found in the far field of supersonic jets. Further, the data allow the development of a model for the spatial distribution of the sources of the dominant noise components. On applying the model to the high-burn phase of the experiment, excellent agreements are found.